This invention relates to a method of selecting between two operation modes in a dual fuel internal combustion engine of the diesel-type, and to a dual fuel internal combustion engine of the diesel-type operable according to such method.
Dual fuel internal combustion engines of the diesel-type usually comprise a combustion chamber being at least partly delimited by a piston, a first fuel supply for a first fuel, said first fuel supply being located in the combustion chamber or in an inlet port thereof, and a second fuel supply for a second fuel.
A known method to operate internal combustion engines as described above comprises the steps of:
pre-mixing said first fuel in said combustion chamber and/or in said inlet port;
compressing the charge containing the first fuel to conditions close to Homogeneous Charge Compression Ignition (HCCI) of said first fuel; and
injecting a second fuel into said combustion chamber to initiate auto-ignition of said second fuel and subsequently said first fuel.
Such a method may generally be described as an operation mode distinguished by homogeneous ignition and combustion of the remaining fuel. For briefness, in the following such a method will also be referred to as a “homogeneous combustion mode”.
Another known method to operate internal combustion engines as described above comprises the steps of:
Pre-mixing said first fuel in said combustion chamber and/or in said inlet port;
igniting said first fuel in said combustion chamber by injection and auto-ignition of a second fuel to thereby initiate conditions for pre-mixed flame propagation combustion.
Such a method may generally be described as an operation mode distinguished by pre-mixed flame propagation combustion. For briefness, in the following such a method will also be referred to as a “flame propagation mode”.
Different modes of operation of the internal combustion engines present different advantages. There is therefore a need to provide a method for enabling various operation modes to be carried out in an internal combustion engine of the diesel-type.
In view of the above, it will be understood that there is also a need for a dual fuel internal combustion engine of the diesel-type for carrying out a method as desired above.
In accordance with an aspect of the invention there is provided a method of selecting between two operation modes in a dual fuel internal combustion engine of the diesel-type, comprising a combustion chamber being at least partly delimited by a piston, a first fuel supply for a first fuel, said first fuel supply being located in or at the combustion chamber and/or in or at an inlet port thereof, and a second fuel supply for a second fuel,
the engine having two different operation modes, both operation modes comprising the steps of:
pre-mixing said first fuel in said combustion chamber and/or in said inlet port,—compressing the charge containing the first fuel to conditions that allow auto-ignition of the second fuel,
performing a first injection of the second fuel into said combustion chamber to initiate auto-ignition of said second fuel, thereby initiating conditions for combustion of the fuel remaining in the combustion chamber after auto-ignition of the second fuel, wherein
said first operation mode is distinguished by homogeneous ignition and combustion of the remaining fuel,
said second operation mode is distinguished by pre-mixed flame propagation combustion of the remaining fuel,
said method further comprising the step of:
adjusting the amount of the second fuel injected in said first injection of the second fuel, and/or the timing of said first injection of the second fuel, so as to control the combustion chamber temperature and pressure after auto-ignition of the second fuel such that selection between said first and second operation modes is achieved.
Advantageously, said first fuel is pre-mixed for instance with air and/or recycled exhaust gas, to form the charge containing the first fuel.
The method using the first operation mode is characterised by homogeneous ignition and combustion of the remaining fuel. For briefness, in the following such a method will also be referred to as a “homogeneous combustion mode”.
The method using the second operation mode is characterised by pre-mixed flame propagation combustion of the remaining fuel. For briefness, in the following such a method will also be referred to as a “flame propagation mode”.
In the proposed method, both operation modes may occur in the combustion chamber of the engine. For selecting between the two operation modes, it has been found that the amount of fuel in the first injection of the second fuel may be used so as to control the combustion chamber temperature and pressure after auto-ignition of the second fuel. The temperature and pressure in the combustion chamber will affect which one of the first and the second operation modes that will prevail in the combustion chamber. Hence, a switch between the first and the second operation modes may be achieved by varying the amount of the second fuel injected in said first injection.
Selection of said first operation mode may be performed for instance by increasing the amount of fuel in said first injection of the second fuel and thereby increasing the temperature and pressure in the combustion chamber after auto-ignition of the second fuel. Hence, increasing the amount of second fuel in said first injection may be performed in order to switch from the second operation mode to the first operation mode. Moreover, further increasing the amount of the second fuel injected in said first injection may be performed in order to move an already prevailing first operation mode to operation parameters being farther from the switching point. Preferably, the amount or quantity of the first injection of the second fuel in said first injection is controlled by using a device for determining the desired operation mode.
Preferably, the amount of the second fuel injected in said first injection of the second fuel may be above a predetermined threshold amount for selecting said first operation mode.
Selection of said second operation mode may be performed for instance by decreasing the amount of fuel in said first injection of a second fuel. Hence, decreasing the amount of second fuel in said first injection may be performed in order to switch from the first operation mode to the second operation mode. Moreover, further decreasing the amount of the second fuel injected in said first injection may be performed in order to move an already prevailing second operation mode to operation parameters being farther from the switching point. Preferably, the amount or quantity of the first injection of the second fuel in said first injection is controlled by using a device for determining the desired operation mode.
Preferably, the amount of the second fuel injected in said first injection of the second fuel may be below a predetermined threshold amount for selecting said second operation mode.
Alternatively or in combination with variations of the amount of the second fuel injected in a first injection of the second fuel, the timing (i.e. the point in time when injection starts and the duration of the injection) of the first injection of the second fuel can be varied to select one of the two operation modes. A selection of the first operation mode can be made by arranging (i.e. by selecting the timing of injection) the auto-ignition of the second fuel to occur when the piston of the engine is close to a top dead position. A selection of the second operation mode can be made by arranging the auto-ignition of the second fuel to occur when the piston of the engine is farther from a top dead position.
The switching between said first and second modes may advantageously be performed by controlling the amount of second fuel injected, and/or the timing of the injection of the second fuel, when the lambda value (normalised air/fuel ratio) in the combustion chamber is between 1 and 3, preferably between 1.5 and 2.5, most preferably approximately 2.
Preferably, the first fuel is a fuel with high octane number, preferably greater than 90.
Advantageously, the first fuel is a gaseous fuel, preferably natural gas or biogas.
Preferably, the second fuel is a fuel with high cetane number, preferably greater than 40. Advantageously, said second fuel is a liquid fuel, preferably diesel oil, bio-diesel or DME (dimethyl ether).
Advantageously, said first fuel is pre-mixed for instance with air and/or recycled exhaust gas.
In a second aspect of the invention there is provided a dual fuel internal combustion engine of the diesel-type comprising:
a combustion chamber, being at least partly delimited by a piston,
a first fuel supply for a first fuel, said first fuel supply being located in or at the combustion chamber and/or in or at an inlet port thereof,
a second fuel supply for a second fuel,
said first fuel being pre-mixed in said combustion chamber and/or said inlet port, at least one device for compressing the charge containing the first fuel to conditions that allow auto-ignition of the second fuel,
at least one injector device for performing a first injection of the second fuel into said combustion chamber to initiate auto-ignition of said second fuel, thereby initiating conditions for combustion of the fuel remaining in the combustion chamber after auto-ignition of the second fuel, wherein
said first operation mode is distinguished by homogeneous ignition and combustion of the remaining fuel,
said second operation mode is distinguished by pre-mixed flame propagation combustion of the remaining fuel.
The dual fuel internal combustion engine comprises further at least one injector device for adjusting the amount of the second fuel injected in said first injection of the second fuel, and/or the timing of said first injection of the second fuel, so as to control the combustion chamber temperature and pressure after auto-ignition of the second fuel such that selection between said first and second operation modes is achieved. In applying this principle, it is possible to switch between said first and second operation modes of such a dual fuel internal combustion engine.
In a preferred embodiment of the dual fuel internal combustion engine of the diesel-type according to an aspect of the invention, the at least one injector device for performing of the first injection of the second fuel is adapted to
in the first operation mode of said engine, performing said first injection of the second fuel into said combustion chamber to initiate auto-ignition of said second fuel and subsequently said first fuel in said combustion chamber, thereby initiating conditions for homogeneous ignition and combustion of the first fuel, and
in the second operation mode of said engine, performing said first injection of the second fuel into said combustion chamber to initiate auto-ignition of said second fuel for igniting said first fuel in said combustion chamber, thereby initiating conditions for pre-mixed flame propagation combustion of the first fuel.
Auto-ignition typically occurs soon after the start of injection of the second fuel. Initially, a fraction of the second fuel auto-ignites, and generally a substantial amount of the second fuel is combusted before auto-ignition of the first fuel starts. Hence, the term “subsequently” used above relates to the start of the auto-ignition process and does not exclude that a portion of the auto-ignition of the first and of the second fuel, respectively, may take place in parallel. Typically, a first portion of the second fuel is combusted before auto-ignition of the first fuel starts and then the remaining second portion of the second fuel is combusted in parallel to the combustion of the first fuel.
It will be understood that features and advantages as described above in relation to the method are equally applicable to the dual fuel internal combustion engine in accordance with aspects the invention.
First Mode of Operation
Returning to the first operation mode of the engine, a preferred embodiment of said first operation mode will be described in the following.
The first operation mode of the engine may advantageously comprise a method of operating a dual fuel internal combustion engine of the diesel-type, comprising a combustion chamber being at least partly delimited by a piston, a first fuel supply for a first fuel, said first fuel supply being located in or at the combustion chamber and/or in or at an inlet port thereof, and a second fuel supply for a second fuel, the method comprising the steps of:
pre-mixing said first fuel in said combustion chamber and/or in said inlet port,
compressing the charge containing the first fuel to conditions close to homogeneous charge compression ignition of said first fuel,
performing a first injection of the second fuel into said combustion chamber to initiate auto-ignition of said second fuel and subsequently said first fuel.
Further, the first operation mode may advantageously comprise the step of:
performing at least one subsequent, preferably liquid, injection, said subsequent injection supplying additional kinetic energy into the combustion process to thereby enhance late mixing in the combustion chamber, so as to improve late oxidation during combustion.
The additional kinetic energy provided by the subsequent injection (or subsequent injections) is preferably supplied in later stages of the combustion cycle so as to enhance global and local mixing for improved late oxidation.
The subsequent injection (or subsequent injections) enhances combustion in low temperature regions of the combustion chamber, such as close to the walls thereof, by improving the mixing between low and high temperature regions. Accordingly, the combustion is improved leading to better fuel efficiency and less emission.
The first injection of the second fuel into the combustion chamber is sufficient to initiate auto-ignition of the first fuel. In contrast, the purpose of the subsequent injection (or subsequent injections) (after said first injection of second fuel) is to add kinetic energy creating increased mixing in the combustion chamber. Accordingly, the subsequent injections need not necessarily add any fuel to the combustion process. Any gaseous or liquid matter, which may transfer kinetic energy via an injection thereof and which does not disturb the combustion process, may be used.
It is preferred to inject a liquid for the subsequent injections, since the necessary quantity of supplied kinetic energy and the administration of the injections may generally be easier to achieve with liquids than with injection of gaseous matter. In view of the above, any liquid which does not disturb the combustion process could be injected, such as e.g. water. It is to be understood however, that with injection of a liquid is meant that the substance is in its liquid phase at the precise moment of injection. Once injected, the liquid will, for typical conditions, transfer to gaseous phase with a rate depending on the combustion chamber conditions, the injection process and the properties of the liquid. Hence, even when the subsequent injections are liquid injections, a large fraction of the kinetic energy is transferred and a large fraction of the turbulence is created by impact of the injected substance while in its gaseous phase.
However, for practical purposes, it is preferred that the at least one subsequent injection is an injection of a fuel. Most preferred, the subsequent liquid injection is of the same fuel as the first injection, that is, of the second fuel. As such, no additional constructive or engine design arrangements for the subsequent injections are necessary.
Preferably, the amount of additional kinetic energy supplied by the at least one subsequent injection is variable.
As mentioned above, it is envisaged to use a combustion cycle comprising at least one subsequent injection, but several subsequent injections may also be used.
Advantageously, the amount of additional kinetic energy supplied by these subsequent injections is variable by varying at least one of the number of subsequent injections, the injection pressures of the subsequent injections, the durations of the subsequent injections, or the dwell time between subsequent injections. In this context it is to be understood that the amount of additional kinetic energy supplied may be varied between subsequent injections of the same combustion cycle, and/or be varied between subsequent injections belonging to different combustion cycles.
Advantageously, the amount of kinetic energy supplied by these subsequent injections is varied in accordance with feedback supplied from at least one sensor sensing at least one of: the combustion process, the fuels and their parameters as temperature, pressure, time, quality of fuel, etc. and/or the results of said combustion process including but not limited to the resulting chemical compounds produced by such combustion process and contained in the exhaust gas of the engine. The control of the at least one subsequent injection may then be performed using feedback from said sensor as input. Accordingly, the combustion process may be continuously surveyed and the subsequent injections continuously controlled to improve said combustion process. Advantageously, in a start-up phase a first combustion cycle or a first few combustion cycles may be run using selected start parameters for the subsequent injection, whereafter the sensor is used for evaluating said first combustion cycle or the first few combustion cycles, and providing input for the adjustment of the subsequent injection for the following combustion cycles in the normal operational phase of the engine. Accordingly, the combustion process may be adapted for a specific situation. Moreover, this enables a more robust combustion process, since the subsequent injections may also be adapted if the conditions should vary during continuous operation of the engine.
As an alternative to initiating the first combustion cycle or the first few combustion cycles with selected start parameters for the subsequent injection (or subsequent injections), in the start-up phase the first combustion cycle or the first few combustion cycles could be run without any subsequent injection at all.
The sensor(s) may advantageously be sensor(s) for sensing for instance CO or HC concentrations in the engine exhaust gas.
Alternatively, in addition or in combination with one or more CO or HC sensors, the method may use a sensor for sensing the quality of the combustion. Various such sensors may be applicable. Preferably, a device for sensing the combustion chamber pressure could be used in combination with a method for a fast evaluation (on a cycle-to-cycle basis) of the heat release.
In a second aspect of the invention, concerning the first operation mode, there may advantageously be provided a dual fuel internal combustion engine of the diesel-type comprising:
a combustion chamber being at least partly delimited by a piston,
a first fuel supply for a first fuel, said first fuel supply being located in or at the combustion chamber and/or in or at an inlet port thereof,
a second fuel supply for a second fuel,
said first fuel being pre-mixed in said combustion chamber and/or said inlet port,
at least one device for compressing the charge containing the first fuel to conditions close to homogeneous charge compression ignition of said first fuel,
at least one injector device for performing a first injection of the second fuel into said combustion chamber to initiate auto-ignition of said second fuel and subsequently said first fuel.
Advantageously, the dual fuel internal combustion engine further comprises at least one injector device for performing at least one subsequent preferably liquid, injection, so as to supply additional kinetic energy into the combustion process to thereby enhance late mixing in the combustion chamber, so as to improve late oxidation during combustion.
Preferably, the dual fuel combustion engine comprises at least one sensor for determining the operation mode, wherein output from said sensor is used to control the amount or quantity of the first injection of the second fuel, and/or the timing of said first injection of the second fuel.
Preferably, the dual fuel combustion engine comprises at least one sensor for providing feedback from the combustion process, wherein the output from said sensor is used for said control of the at least one subsequent (preferably liquid) injection.
Preferably, the dual fuel combustion engine comprises a sensor for sensing the quality of the combustion, or the quality of the supplied fuel.
Second Operation Mode
Returning now to the second operation mode, advantageous embodiments of said operation mode will be described in the following.
Advantageously, for the second operation mode, there may be provided a method of operating an internal combustion engine of the diesel-type, comprising a combustion chamber being at least partly delimited by a piston, a first fuel supply for a first fuel, said first fuel supply being located in or at the combustion chamber and/or in or at an inlet port thereof, and a second fuel supply for a second fuel, the method comprising the steps of:—pre-mixing said first fuel in said combustion chamber and/or in said inlet port,
compressing the charge containing the first fuel to conditions that allow auto-ignition of the second fuel,
performing a first injection of the second fuel into said combustion chamber to initiate auto-ignition of said second fuel for igniting said first fuel, thereby initiating conditions for pre-mixed flame propagation combustion of the first fuel.
Further, the second operation mode may advantageously comprise the step of:
performing at least one subsequent, preferably liquid, injection, said subsequent injection supplying additional kinetic energy into the combustion process to thereby enhance turbulence intensity and propagation speed of said flame and/or to enhance late mixing in the combustion chamber, so as to improve late oxidation during combustion of the remaining fuel.
The additional kinetic energy provided by the subsequent injection (or subsequent injections) may be used to create additional small-scale turbulence in the region of the flame in the combustion chamber, which in turn enhances the propagation speed of said flame. Accordingly, the flame front will develop faster and reach into the combustion chamber in shorter time than without such additional turbulence, resulting in a more favourable combustion chamber pressure development over time, resulting in turn in higher (fuel) efficiency of the engine and less risk for knock compared with conventional dual fuel combustion processes without this additional turbulence.
Alternatively, or in addition to a subsequent injection to create additional turbulence, a subsequent injection (or subsequent injections) may be used for enhancing late mixing in the combustion chamber so as to improve final oxidation during combustion. Such a subsequent injection may be referred to as a “post-injection”. The purpose of the post-injection is, as the purpose of the previously described subsequent injections, to add kinetic energy to the combustion process. However, the kinetic energy added by the post-injection will not primarily be utilised as to increase the flame speed. Instead, the kinetic energy from the post-injection is supplied so as to create turbulence in the later stages of the combustion cycle and hence enhance late or global mixing of gases remaining in the combustion chamber for improving late oxidation during the combustion of the fuel.
The first injection of the second fuel is sufficient to initiate ignition and hence to initiate pre-mixed flame propagation combustion. In contrast, the purpose of the subsequent injection (or subsequent injections) (after said first injection of the second fuel) is to add kinetic energy creating additional small scale turbulence in the region of the propagating
flame or enhancing global mixing of gases in the combustion chamber. Accordingly, the subsequent injections need not necessarily add any fuel to the combustion process. Any gaseous or liquid matter, which may transfer kinetic energy via an injection thereof and which does not disturb the combustion process, may be used.
It is preferred to inject a liquid for the subsequent injections, since the necessary quantity of supplied kinetic energy and the administration of the injections may generally be made easier to achieve with liquids than with injection of gaseous matter. In view of the above, any liquid which does not disturb the combustion process could be injected, such as e.g. water. It is to be understood however, that with injection of a liquid is meant that the substance is in its liquid phase at the precise moment of injection. Once injected, the liquid will, for typical conditions, transfer to gaseous phase with a rate depending on the combustion chamber conditions, the injection process and the properties of the liquid. Hence, even when the subsequent injections are liquid injections, a large fraction of the kinetic energy is transferred and a large fraction of the turbulence is created by impact of the injected substance while in its gaseous phase.
However, for practical purposes, it is preferred that the subsequent injection is an injection of a fuel. Most preferred, the subsequent liquid injection is of the same fuel as the first injection, that is, of the second fuel. As such, no additional constructive or engine, design arrangements for the subsequent injections are necessary.
Preferably, the amount of additional kinetic energy supplied by the at least one subsequent injection is variable.
Advantageously, the amount of additional kinetic energy supplied by these subsequent injections is variable by varying at least one of: the number of subsequent injections, the injection pressures of the subsequent injections, the durations of the subsequent injections, or the dwell time between subsequent injections. In this context it is to be understood that the amount of additional kinetic energy supplied may be varied between subsequent injections of the same combustion cycle, and/or be varied between subsequent injections belonging to different combustion cycles.
Advantageously, the amount of kinetic energy supplied by these subsequent injections is varied in accordance with feedback supplied from at least one sensor sensing at least one of: the combustion process, the fuels and their parameters as temperature, pressure, time, quality of fuel, etc. and/or the results of said combustion process including but not limited to the resulting chemical compounds produced by such combustion process and contained in the exhaust gas of the engine. The control of the at least one subsequent injection may then be performed using feedback from said sensor as input. Accordingly, the combustion process may be continuously surveyed and the subsequent injections continuously controlled to improve said combustion process. Advantageously, in a startup phase a first combustion cycle or a first few combustion cycles may be run using selected start parameters for the subsequent injection, whereafter the sensor is used for evaluating said first combustion cycle or the first few combustion cycles, and providing input for the adjustment of the subsequent injection for the following combustion cycles in the normal operational phase of the engine. Accordingly, the combustion process may be adapted for a specific situation. Moreover, this enables a more robust combustion process, since the subsequent injections may also be adapted if the conditions should vary during continuous operation of the engine.
As an alternative to initiating the first combustion cycle or the first few combustion cycles with selected start parameters for the subsequent injection, in the start-up phase the first combustion cycle or the first few combustion cycles could be run without any subsequent injection at all.
The sensor(s) may advantageously be sensor(s) for sensing for instance the quality of the supplied fuel, preferably for sensing the octane number. Such sensors could be provided e.g. in the fuel tank or fuel supply system.
Alternatively, in addition or in combination with such a fuel quality sensor, the method may use a sensor for sensing the quality of the combustion. Various such sensors may be applicable. One known type of sensor is a so called knock-sensor. Preferably, a device for sensing the combustion chamber pressure could be used in combination with a method for a fast evaluation (on a cycle-to-cycle basis) of the heat release.
Regarding the second aspect of the invention, and concerning said second operation mode, there may be provided a dual fuel internal combustion engine of the diesel-type, comprising:
a combustion chamber being at least partly delimited by a piston,
a first fuel supply for a first fuel, said first fuel supply being located in or at the combustion chamber and/or in or at an inlet port thereof,
a second fuel supply for a second fuel,
said first fuel being pre-mixed in said combustion chamber and/or said inlet port,—at least one device for compressing the charge containing the first fuel to conditions that allow auto-ignition of the second fuel,
at least one injector device for performing a first injection of the second fuel into said combustion chamber to initiate auto-ignition of said second fuel for igniting said first fuel, thereby initiating conditions for pre-mixed flame propagation combustion of the first fuel.
Advantageously, the dual fuel combustion engine further comprises at least one injector device for performing at least one subsequent (preferably liquid) injection, so as to supply additional kinetic energy into the combustion process to thereby enhance turbulence intensity and propagation speed of said flame and/or to enhance late mixing in the combustion chamber, so as to improve late oxidation during combustion of the remaining fuel.
Preferably, the dual fuel combustion engine comprises at least one sensor for determining the operation mode, wherein output from said sensor is used to control the amount or quantity of the first injection of the second fuel, and/or the timing of said first injection of the second fuel.
Preferably, the dual fuel combustion engine comprises at least one sensor for providing feedback from the combustion process, wherein the output from said sensor is used for said control of the at least one subsequent (preferably liquid) injection.
Preferably, the dual fuel combustion engine comprises a sensor for sensing the quality of the combustion, or the quality of the supplied fuel.
It should be realised that alternatives and advantages as described above in relation to the various methods applies equally to the various dual fuel combustion engines according to aspects of the invention.